I'm looking at using an AD9833 DDS sine/square/triangle wave generator. At 25MHz clock, it goes up to 12.5MHz output, although the output likely isn't that great at 1/2 the clock. But that has only 0.1Hz frequency resolution, and the XO on the board isn't that great.

So I'm thinking of replacing it with a TCXP 1MHz 0.5ppm oscillator. That should still have clean sine waves at 200kHz and have a resolution of 0.004Hz.

The AD9833 has 28 bit resolution on frequency and a 10 bit DAC. It can be used as a sweep frequency generator. It has outputs for sine, triangle, and square wave. You can get it on a breakout board with SMA connector for $12 to $15 USD.

Page 12 of the datasheet shows an example of a 60kHz output with the first harmonic about 62dB down from the fundamental.AD9833 Datasheet

A swept frequency output can be used to measure amplifier and filter response. Or a white noise source and you can get sound cards that capture at 192ksps @ 24 bit, and software that can use that for a pretty good audio spectrum analyzer. Some include the ability to use one channel as an output to provide a swept sine wave, and the other as an input at the same time. Both your sound card and the software must support this.

To reduce harmonic distortion of the sine wave, perhaps a tuneable lowpass filter that stays just above the output frequency.

I'll have to see how even the output of the AD9833 stays as frequency changes. The AD9850 and AD9851 have a problem with the output dropping as frequency rises, so people have designed gain control in to keep the signal level stable.

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